This study is aimed at providing data on the effects of child spacing and family size on mental health (coping ability) so that each American can make an informed judgment regarding the quality of individuals produced by alternative family sizes and sibling age-gaps. An additional sizable contribution to population-planning knowledge will be normative tables for middle- and lower-class populations showing frequency of child-spacing age-gaps and family sizes. The birth dates of the subject and of each of his siblings will be obtained from existing records and from interviews. In three of the designs, lack of mental health (difficulty in coping) will be defined operationally as under psychiatric care or in classes for learning-and-behavior difficulties. Those with coping problems will be compared with those not identified, and significance of difference in rates of incidence of size of family and length of sibling age-gap will be determined. In the fourth design, school achievement or academic aptitude will be used as indices of coping ability. An analysis of variance will be done for school marks by size of family, sib age-gap, and close sib's sex. The fifth design is aimed at finding correlates of coping (demographic) by children from large families and by those separated by short age-gaps.